feat: add listening property in the server interface

[fernandobastos]

• Add listening property to Server
• Update start and stop methods in RestServer/RPCServer to use the new property

fix #1368

Checklist

• npm test passes on your machine
• New tests added or existing tests modified to cover all changes
• Code conforms with the style guide
• API Documentation in code was updated
• Documentation in /docs/site was updated
• Affected artifact templates in packages/cli were updated
• Affected example projects in examples/* were updated

[raymondfeng]

@fernandobastos Thanks for the patch.

To be consistent, please also update https://github.com/strongloop/loopback-next/blob/master/packages/http-server/src/http-server.ts to use listening instead of _started.

[raymondfeng]

@fernandobastos Please sign CLA too - https://cla.strongloop.com/agreements/strongloop/loopback-next

[raymondfeng]

It should be private _listening: boolean and add a get function to expose the value so that it's readonly.

private _listening: boolean = false;
get listening() {
  return this._listening;
}

You should replace get started() with get listening().

[raymondfeng]

Please fix the listening in http-server module. There is also a build error:

packages/http-server/src/http-server.ts(121,17): error TS2551: Property '_started' does not exist on type 'HttpServer'. Did you mean 'started'?

[raymondfeng]

@fernandobastos Please fix the build error:

packages/http-server/src/http-server.ts(121,17): error TS2339: Property '_started' does not exist on type 'HttpServer'.

[raymondfeng]

Please squash the commit into one.

[bajtos]

@fernandobastos thank you for the contribution ❤️